Bifunctional carbohydrate biopolymers entrapped lipase as catalyst for the two consecutive conversions of α-pinene to oxy-derivatives

Improving efficiency and reducing enzyme inactivation during lipase-mediated epoxidation of α-pinene in a double-phase reaction system

Chemoenzymatic epoxidation of olefin mediated by lipase is a green and environmentally friendly alternative process. However, the mass transfer barrier and lipase deactivation caused by the traditional organic-water biphasic reaction system have always been the focus of researchers' attention. To overcome these issues, we investigated the effects of reaction temperature and two important substrates (H₂O₂ and acyl donor) on the epoxidation reaction and interfacial mass transfer. As a result, we determined the optimal reaction conditions: a temperature of 30 °C, 30 wt-% H₂O₂ as the oxygen source, and 1 M lauric acid as the oxygen carrier. Additionally, by simulating the conditions of shaking flask reactions, we designed a batch reactor and added a metal mesh to effectively block the direct contact between high-concentration hydrogen peroxide and the enzyme. Under these optimal conditions, the epoxidation reaction was carried out for 5 h, and the product yield reached a maximum of 93.2%. Furthermore, after seven repetitive experiments, the lipase still maintained a relative activity of 51.2%.

Glutaraldehyde-crosslinked Rhizopus oryzae whole cells show improved catalytic performance in alkene epoxidation

BACKGROUND

Existing methods for alkene epoxidation are based on lipase-catalysed perhydrolysis. However, the inactivation of the expensive lipase enzyme is problematic for enzymatic epoxidation at large scales due to the use of hydrogen peroxide and peracids at high concentrations in the reaction. The immobilisation of whole cells appears to be a promising approach to alleviate this problem.

RESULTS

A green oxidation system containing hydrogen peroxide, Na₃C₆H₅O₇, an acyl donor, and glutaraldehyde (GA)-crosslinked cells of Rhizopus oryzae was developed for the epoxidation of alkenes. GA-crosslinked cells of Rhizopus oryzae were adopted as a biocatalyst into the epoxidation system. A variety of alkenes were oxidised with this system, with a 56-95% analytical yield of the corresponding epoxides. The catalytic performance of the crosslinked treated cells was substantially improved compared to that of the untreated cells and the initial reaction rate increased from 126.71 to 234.72 mmol/L/h, retaining 83% yields even after four batches of reactions. The addition of 3.5 mmol Na₃C₆H₅O₇ not only acts as an acid-trapping reagent to eliminate the negative effect of the carboxylic acid on the alkene oxide but also forms a saturated salt solution with the aqueous phase, affecting the concentration of H₂O₂ in the three phases and thus the epoxidation reaction. Organic solvents with a logP value > 0.68 were good at producing hydroxy peracids; however, this method is only suitable for oxidation in a two-liquid phase.

CONCLUSIONS

Compared with other lipase biocatalysts, the GA-crosslinked whole-cell biocatalyst is inexpensive, readily available, and highly stable. Therefore, it can be considered promising for industrial applications.

Polymer/Enzyme Composite Materials—Versatile Catalysts with Multiple Applications

A significant interest was granted lately to enzymes, which are versatile catalysts characterized by natural origin, with high specificity and selectivity for particular substrates. Additionally, some enzymes are involved in the production of high-valuable products, such as antibiotics, while others are known for their ability to transform emerging contaminates, such as dyes and pesticides, to simpler molecules with a lower environmental impact. Nevertheless, the use of enzymes in industrial applications is limited by their reduced stability in extreme conditions and by their difficult recovery and reusability. Rationally, enzyme immobilization on organic or inorganic matrices proved to be one of the most successful innovative approaches to increase the stability of enzymatic catalysts. By the immobilization of enzymes on support materials, composite biocatalysts are obtained that pose an improved stability, preserving the enzymatic activity and some of the support material’s properties. Of high interest are the polymer/enzyme composites, which are obtained by the chemical or physical attachment of enzymes on polymer matrices. This review highlights some of the latest findings in the field of polymer/enzyme composites, classified according to the morphology of the resulting materials, following their most important applications.

Solvent screening, optimization and kinetic parameters of the biocatalytic epoxidation reaction of β-pinene mediated by Novozym®435

Monoterpenes, such as beta-pinene, are secondary metabolites widely used in the flavors and fragrance industries and can have their structure altered to enhance their applicability, such as producing epoxides, which are used as intermediaries for pharmaceuticals. Epoxides are commonly synthesized by the use of inorganic acids as catalysts, although the acid medium induces epoxide degradation. To overcome these limitations biocatalysis is shown as an alternative. Related to, this work aimed to perform the synthesis of β-Pinene epoxide using Pseudozyma antarctica lipase B (Novozym®435) as a biocatalyst, while determining the independent variables that influence the reaction using experimental design tools. Different solvent systems were evaluated (cyclohexane, acetonitrile, ethyl acetate, and dichloromethane) until 72 h reaction time, from which ethyl acetate showed higher conversion into the epoxidized product (40% in 24 h). Under the other solvents systems, several oxidized by-products were obtained, such as ketones and aldehydes. Moreover, applying metrics of green chemistry, ethyl acetate was also corroborated as the most promising solvent, with a higher atom economy (66.8%) in comparison to the others (41.3%), and a smaller E-value (1.19). Ethyl acetate was the solvent/acyl donor of choice and had the molar ratio and percentage of biocatalyst increased, which resulted in 80% of the product after 3 h of reaction. To obtain an optimized model, four independent variables (temperature, stirring, molar ratio, percentage of biocatalyst) were evaluated using experimental design tools, Fractional Factorial Design and Central Composite Rotatable Design, with conversions ranging from 23 to 95% after 3 h. All the independent variables were statistically significant (p < 0.05) and had different degrees of impact on the conversion. Kinetic parameters of the reaction were determined using the Lineweaver-Burk model (results under 30.1 mmol for Km and 10.7 mmol.min^-1 for Vmax). In conclusion, the combination of two different tools of experimental design provided the development of an optimized model for beta-Pinene epoxidation, achieving high conversion to the epoxidized product after 3 h.

Recent Trends in Biomaterials for Immobilization of Lipases for Application in Non-Conventional Media

The utilization of biomaterials as novel carrier materials for lipase immobilization has been investigated by many research groups over recent years. Biomaterials such as agarose, starch, chitin, chitosan, cellulose, and their derivatives have been extensively studied since they are non-toxic materials, can be obtained from a wide range of sources and are easy to modify, due to the high variety of functional groups on their surfaces. However, although many lipases have been immobilized on biomaterials and have shown potential for application in biocatalysis, special features are required when the biocatalyst is used in non-conventional media, for example, in organic solvents, which are required for most reactions in organic synthesis. In this article, we discuss the use of biomaterials for lipase immobilization, highlighting recent developments in the synthesis and functionalization of biomaterials using different methods. Examples of effective strategies designed to result in improved activity and stability and drawbacks of the different immobilization protocols are discussed. Furthermore, the versatility of different biocatalysts for the production of compounds of interest in organic synthesis is also described.

Immobilized enzymes: understanding enzyme – surface interactions at the molecular level

Interactions between immobilized enzymes and supporting surfaces are complex and context-dependent and can significantly alter enzyme structure, stability and activity.

Novel chemoenzymatic oxidation of amines into oximes based on hydrolase-catalysed peracid formation

The efficient transformation of benzylamines into the corresponding oximes has been described by means of a chemoenzymatic process.